1. Field of the Invention
The present invention relates to an image forming apparatus using electrophotography, such as, for instance, a copying machine, a printer, a fax device, or a multifunction device comprising the foregoing, and more particularly to a developer supply device for supplying a two-component developer comprising a toner and a carrier to a developing unit, and relates to a developer container and a developer used in this developer supply device.
2. Description of the Related Art
Conventional image forming apparatuses using electrophotography, such as copying machines, printers and the like, use known technologies (for instance, as disclosed in Japanese Unexamined Patent Application Laid-open No. 2001-194860) in which developer is replaced by suitably replenishing a fresh two-component developer into a developing unit (developing device) that holds a two-component developer comprising a toner and a carrier (including developers where an additive or the like is added), this system being called the trickle developing system.
In developing devices using two-component developers, toner is suitably replenished into the developing device through an opening provided on part of the developing device, in accordance with toner consumption in the developing device. The replenished toner is stirred and mixed, through the action of a stirring member such as a transport screw or the like, with the developer inside the developing device. Part of the stirred/mixed developer is supplied to a developing roller. The amount of developer supported on the developing roller is suitably adjusted by a doctor blade, after which the toner in the two-component developer adheres to a latent image on a photosensitive drum at a position opposite the photosensitive drum.
During an ordinary developing process, thus, the carrier in the two-component developer held in the developing device remains inside the developing device without becoming consumed, and, as a result, the carrier deteriorates over time. Specifically, the stirring and mixing of the carrier inside the developing device over longs periods of time gives rise to a “film shaving phenomenon” that involves wear and/or delamination of the carrier coating, thereby lowering the charge power of the carrier, and a “spent phenomenon” in which the components of the toner and/or additives adhere to the surface of the carrier thereby lowering the charge power of the latter.
Trickle developing is a developing method for preventing loss of image quality in output images resulting from such degradation of the carrier over time. Specifically, fresh two-component developer (premix toner) is suitably replenished into the developing device, while part of the two-component developer held in the developing device is suitably discharged out of the developing device, thereby reducing degraded carrier in the developing device and maintaining the amount of developer held in the developing device, and preserving the charge power of the developer.
Image forming apparatuses using trickle developing afford a more stable output image quality over time than apparatuses in which the developing device and/or the developer must be replaced by new ones whenever the carrier deteriorates over time.
Japanese Unexamined Patent Application Laid-open No. 2004-29306 discloses a technology of an image forming apparatus using trickle developing, in which a two-component developer having, for instance, prescribed blending ratios of toner and carrier, is held in a bolt-shaped developer container having spiral protrusions on the inner wall thereof. In technologies such as the one of Japanese Unexamined Patent Application Laid-open No. 2004-29306, the developer is discharged from an opening through rotational driving of the bottle-shaped developer container.
Japanese Unexamined Patent Application Laid-open No. 2002-214894 discloses a toner-replenishing device for transporting toner contained in a toner-holding container to a developing device, using a screw pump (Mohno pump). Specifically, a flexible toner-holding container is removably installed in the image forming apparatus body. The toner-holding container arranged in the apparatus body is connected to a tube via a nozzle having a toner discharge outlet. One end of the tube is connected to the screw pump. The screw pump comprises, for instance, a rotor, a stator, an inlet, a universal joint, and a motor. Negative pressure (suction pressure) is formed inside the tube as a result of the rotation of the rotor inside the stator in a predetermined direction, through the action of the motor, whereby the toner held in the toner-holding container is discharged out of the toner discharge outlet and moves inside the tube together with air. The toner moving inside the tube is suctioned through the inlet of the screw pump, is then fed into the gaps between the stator and the rotor, and is sent to the other end along with the rotation of the rotor. The fed toner is discharged through the feeding outlet of the screw pump, and is replenished into the developing device.
In such a toner replenishing device, the toner transport channel between the toner-holding container, as a toner supply source, and the developing device to which the toner is supplied, can be formed of a flexible tube, which, as is known, increases the degree of freedom for configuring the layout of the overall image forming apparatus. Specifically, a toner replenishing device using a screw pump transports toner as a result of pressure generated inside the flexible tube through suction of air out of the tube. This allows setting relatively freely the layout of the toner-holding container, the developing device and the toner supply channel, and allows thus reducing the size of the image forming apparatus.
In the technology disclosed in the above-described Japanese Unexamined Patent Application Laid-open No. 2004-29306 and the like, the specific gravity of the carrier is larger than the specific gravity of the toner, which made separation of the toner and the carrier very likely during the rotation of the bottle-shaped developer container. Image quality such as image density and the like may be become unstable when the proportions of toner and carrier (toner concentration) cannot be kept constant in the developer that is being transported towards the developing device. Also, toner aggregates may also form during the rotation of the bottle-shaped developer container, which may give rise to abnormal images such as white spots and the like.
In order to solve such problems, it would be conceivable to use the technology of, for instance, the above Japanese Unexamined Patent Application Laid-open No. 2002-214894, and transport together air and a developer (premix toner) in which a toner and a carrier are mixed beforehand, using a pump such as an air pump or a screw pump. Since there would be no rotational driving of the developer container in which the developer is held, no toner aggregates would form, and the developer would not undergo mechanical stresses, thus reducing the likelihood of problems such as toner and carrier separation.
In such a case, however, the developer held in the flexible developer container must be discharged stably. That is, if the carrier gap in the developer container is insufficient, it is highly probable that the developer cannot be supplied (discharged) stably from the developer container, but providing the above-described gap in a sufficient manner results in the developer container having a larger size.
Technologies relating to the present invention are also disclosed in, e.g., Japanese Unexamined Patent Application Laid-open No. 2005-195755.